Induction of UDP-Glucose:Salicylic Acid Glucosyltransferase in Oat Roots

Abstract

A UDP-glucose:salicylic acid 3-0-glucosyltransferase (EC 2.4.1.35) (GTase) from oat (Avena sativa L. cv Dal) root extracts was assayed in vitro using [14C]salicylic acid (SA) and an ion exchange column to separate SA from #-glucosylsalicylic acid. The GTase, present at a very low constitutive level, was inducible to 23 times the constitutive level. When excised roots were exposed to SA at pH 6.5, the specific activity of the enzyme increased within 1.5 h, peaked after 8 to 10 h, and then declined. The increase in specific activity depended on the concentration of SA in the induction medium. Among 16 phenolics and phenolic derivatives tested, GTase induction showed high specificity toward SA and acetylsalicylic acid. Specific activity of the enzyme was induced to higher levels in roots from 7-d-old seedlings than roots from younger plants. GTase the induction of the activity of a GTase (2). The GTase catalyzes the formation of GSA, a compound less inhibitory to Cl-absorption than SA (2). The GTase has been partially purified from oat roots, and some of its properties have been described (2, 29). The protein is soluble, has a native Mr of approximately 50,000, has an isoelectric point of approximately 5, and shows high specificity toward UDP-glucose and SA (29). In this paper, we report our initial studies concerning the induction of GTase activity in oat (Avena sativa L.) roots. MATERIALS AND METHODS Plant Material and ChemicalsOat (Avena sativa L. cv Dal) seeds were germinated on cheesecloth stretched over a 4-L beaker containing 3 L of continuously aerated 10 mm CaSO4 in the dark at room temperature. [7-'4C]SA (1.96 GBq mmolV') and [35S]methionine (>40.7 TBq mmol-') were purchased from New England Nuclear and Amersham, respectively. Induction of GTaseRecently, SA4 was identified as a regulator in the flowering of thermogenic Arum lilies (24) and also as a signal molecule in the activation of resistance responses of plants to pathogens (20, 21). These findings stress the need to understand the processes that regulate SA accumulation. Reports of the formation of SA-glucosides in a number of plants (3,7,17) suggest that SA conjugation could play an important role in determining the size of the free SA pool.Ion uptake by cereal roots is inhibited by exogenous applications of SA (9, 10, 12). Oat roots can recover from this inhibition. It 'Abbreviations: SA, salicylic acid; 2-D, two-dimensional; GSA, ,Bglucosylsalicylic acid; GTase, UDP-glucose:salicylic acid 3-O-glucosyltransferase (EC 2.4.1.35); mU, milliunit. 1114Roots from 5-d-old seedlings were excised, rinsed with distilled H20, and incubated in 30 mL g-1 of roots of induction buffer (0.5 mm KCl, 0.25 mm CaSO4, 0.5 mm SA, 25 mM Mes/Tris [pH 6.5]) at 250C for the specific times indicated in 'Results.' SA was added in DMSO to a final DMSO concentration of 0.05% (v/v). SA uptake from the induction solution was measured by a spectrophotometric procedure adopted from Brodie et al. (5). Induction solution (1 mL) was mixed with 1.2 mL of 25 mm Fe2(SO4)3...

Identification of an immediate-early salicylic acid-inducible tobacco gene and characterization of induction by other compounds

“…IEGT was also induced by treatment of cells with certain active SA analogues, such as ASA and BA, but not by the inactive analog, 4HBA. The responses to these compounds demonstrate selectivity among similar molecules and consistency with their degree of activity in other SA responses, such as induction of PR genes [58], competition with SA for binding to catalase (SABP) [7], and induction of UDP-glucose:SA glucosyltransferase activity [62]. Induction was also observed following treatment with M J, a compound which mediates wounding responses in plants, 2,4-D, a synthetic auxin, and H202, another signal molecule for defense responses.…”

Immediate early transcription activation by salicylic acid via the cauliflower mosaic virus as-1 element.

“…Phytotoxicity of SA in the millimolar range may be a barrier to such determinations. UDP-glucose:SA glucosyltransferase is an SA-inducible enzymatic activity in oat roots (Yalpani et al, 1992a(Yalpani et al, , 1992b. Induction of this activity has a threshold of ~10 nM SA and a half-maximal effective concentration of ~100 nM.…”

Salicylic Acid in Rice (Biosynthesis, Conjugation, and Possible Role)

“…Rice roots were grown in an aeroponic system adapted from Yalpani et al (1992). Rice seeds were pre-sterilized in 5% household bleach and germinated in the dark through cheesecloth suspended over an aerated beaker containing 10 mM CaSO,, The roots of 12-d-old seedlings were used for SA-GTase induction studies.…”